What causes spontaneous attachment of files into the 3D model only of a corridor file?

I'm still working in SS10 and recently added the Civil configuration variables to a client's configuration. I create a 2D design file for a corridor, then attach a Civil terrain file (created in a 3D seed file) and an Civil alignment file (2D seed file with 3D model created when profiles added). After I create a corridor, multiple instances (eventually 20+) of the alignment dgn file get spontaneously attached to the 3D model within the corridor file. I have never seen this before. Is there a variable that causes files to automatically be attached? Any ideas what might be causing this? (Power GEOPAK SS10 version 08.11.09.918)